A hematoma, plainly, is a bruise...

A few tiny (or bigger) blood vessels break, and a little (or a lot) of blood pools, creating a red/blue/purple/turning to ugly browns and yellow with time bruise. Anyone who's taken a fall, or had a brother, knows what it's like...

I'm not sure but in my experience (extensive with bruises, less so with cysts thankfully) they look quite different. But because you said it was bruised and slightly black I wouldn't rule it out...